It "seems" to work, in that it appears to shut down my DR800SG and doesn't leave it in some horrible unbootable state.

Using the original simple script I did, it was 92% when I did the shutdown, and 18 hours later when I booted it back up it was still at 92%. So that's good news. Your version is a lot safer than the script I had, but the results should be similar.

I'm going to keep going down the path of putting it into sysd though, mostly just for the fun of doing it.